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aggregation of solid matter composed of one or more of the minerals forming the earth's crust. The scientific study of rocks is called petrology. Rocks are commonly divided, according to their origin, into three major classes—igneous, sedimentary, and metamorphic.
..... Click the link for more information. formed by the consolidation of mud or clay, having the property of splitting into thin layers parallel to its bedding planes. Shale tends to be fissile, i.e., it tends to split along planar surfaces between the layers of stratified rock. Shales comprise an estimated 55% of all sedimentary rocks. The composition of shale varies widely. Shales with very high silica content may have been formed when large quantities of diatomsdiatom
, unicellular organism of the kingdom Protista, characterized by a silica shell of often intricate and beautiful sculpturing. Most diatoms exist singly, although some join to form colonies.
..... Click the link for more information. and volcanic ash were present in the original sediment. Large numbers of fossilsfossil,
remains or imprints of plants or animals preserved from prehistoric times by the operation of natural conditions. Fossils are found in sedimentary rock, asphalt deposits, and coal and sometimes in amber and certain other materials.
..... Click the link for more information. in shales may give them a high calcium content; such shales may grade into limestoneslimestone,
sedimentary rock wholly or in large part composed of calcium carbonate. It is ordinarily white but may be colored by impurities, iron oxide making it brown, yellow, or red and carbon making it blue, black, or gray. The texture varies from coarse to fine.
..... Click the link for more information. . Shales that contain a large percentage of aluminaalumina
or aluminum oxide,
Al2O3, chemical compound with m.p. about 2,000°C; and sp. gr. about 4.0. It is insoluble in water and organic liquids and very slightly soluble in strong acids and alkalies. Alumina occurs in two crystalline forms.
..... Click the link for more information. are used as a source of that mineral in the manufacture of cementcement,
binding material used in construction and engineering, often called hydraulic cement, typically made by heating a mixture of limestone and clay until it almost fuses and then grinding it to a fine powder.
..... Click the link for more information. , and those that contain natural gas and petroleum have become a significant energy resource in the 21st cent. due to the use of hydraulic fracturing techniques in drilling. Shales containing abundant carbonaceous matter grade into bituminous coalcoal,
fuel substance of plant origin, largely or almost entirely composed of carbon with varying amounts of mineral matter. Types
There is a complete series of carbonaceous fuels, which differ from each other in the relative amounts of moisture, volatile matter,
..... Click the link for more information. .
A fine-grained laminated or fissile sedimentary rock made up of silt- or clay-size particles; generally consists of about one-third quartz, one-third clay materials, and one-third miscellaneous minerals, including carbonates, iron oxides, feldspars, and organic matter.
Argillaceous sedimentary rock derived from clays or silts; typically thinly laminated and weak along planes; may be undesirable as a concrete aggregate.
a dark fine-grained laminated sedimentary rock formed by compression of successive layers of clay-rich sediment